What it is: Screenshots are images that appear on the screen, which you can save as a graphic file to use in other documents.
If you see a particularly interesting image on a web page or need to show something that appears on your screen to others, you need to capture a screenshot. While there are many screen capturing programs you can buy, OS X has two ways to capture screenshots quickly and easily.
To capture the whole screen and save the image on your desktop, press Shift+Command+3.
To capture part of the screen, press Shift+Command+4.
To capture just a window, press Shift+Command+4, press the spacebar, and then move the mouse pointer over the window you want to capture and click the mouse.
When you use any of the above methods, you’ll capture a .png file stored on your desktop.
Another way to capture screen images is to use the Grab program, which is buried inside the Utilities folder inside the Applications folder. The Grab program can also capture entire screens or just part of a screen, but it saves files in the .tiff file format and gives you a chance to specify a folder to save your screenshots in.
The best part of the Grab program is that it offers a feature called Timed Screen. The reason to use the Timed Screen option is because if you press the keystrokes needed to capture a screenshot or choose a command from the Grab program to capture a screenshot, it could affect the program currently on your screen that you want to capture.
The Timed Screen option gives you a few seconds between running the Grab program and the time it actually captures the screenshot, including the position of the mouse pointer if you want to capture that as well.
If you need to capture screenshots to put in presentations or for whatever reason, use the Grab program or the Shift+Command+3 (to capture the entire screen) or Shift+Command+4 (to capture part of the screen) methods. Capturing screenshots is fast and easy. Now you just have to find a reason you might need to do it once in a while.